The purpose of this study is as follows: First, to isolate, purify, and immunochemically characterize the surface antigens of Staphylococcus aureus isolated from specimens obtained from human cases of septicemia, osteomyelitis, and deep-seated wounds. Second, to study the immune response in laboratory animals to these surface antigens. Special emphasis will be made to determine the protective properties of the antibodies elicited in the immunized laboratory animals. Third, to determine the immunogenicity of the chemically defined anti-phagocytic antigens in mice, rabbits, bovine, and mini-pigs. Fourth, to determine the feasibility of employing these surface antigens as a means of classifying S. aureus into distinct clinical types. Fifth, to determine the significance of the alternate pathway of complement activation in Staphylococcal diseases. In addition, attempts will be made to determine the chemical structure of the surface components which are involved in the activation of the complement system via the alternate pathway.